Antibody-based therapy is proving very effective in the treatment of various cancers, including solid tumors. For example, HERCEPTIN® has been used successfully to treat breast cancer. Central to the development of a successful antibody-based therapy is isolation of antibodies against cell-surface proteins found to be preferentially expressed on tumor cells. The mesothelin precursor polypeptide is a glycophosphatidylinositol (GPI)-anchored, glycosylated cell surface protein that is proteolytically cleaved to a 30 kDa N-terminal secreted polypeptide and a 40 kDa, C-terminal polypeptide, which predominantly occurs in the membrane-bound, GPI-anchored form (Chang, K. and I. Pastan, Proc. Natl. Acad. Sci. USA, (1996) 93(1):136), and which is named mesothelin herein. Mesothelin is preferentially expressed by certain tumor cells, particularly mesothelioma cells, pancreatic tumor cells and ovarian carcinoma cells, while its expression is limited in normal tissue, making it an ideal target for tumor therapy (Argani, P. et al., Clin. Cancer Res. (2001) 7(12): 3862; Hassan, R., et al., Clin. Cancer Res. (2004) 10(12 Pt 1):3937). The function of mesothelin is unknown, and no apparent reproductive, hematologic, or anatomic abnormalities were observed in mice deficient in mesothelin gene expression (Bera, T. K. and I. Pastan, Mol. Cell. Biol. (2000) 20(8):2902).
Antibody-based, targeted therapy against mesothelin-expressing cancer cells has been proposed for the treatment of lung, ovarian and pancreatic cancer. Mab K1 was the first antibody to membrane-bound mesothelin polypeptide which was described (Chang, K., et al., Int. J. Cancer, (1992) 50(3):373). Mab K1 was generated by immunizing mice. Due to low affinity and poor internalization rates of the antibody, an immunotoxin consisting of Mab K1 linked to a chemically modified truncated form of Pseudomonas exotoxin A was not considered suitable for clinical development (Hassan, R., et al., J. Immunother. (2000) 23(4):473; Hassan, R., et al., Clin. Cancer Res. (2004) 10(12 Pt 1): 3937). Subsequently, single-chain antibodies with higher affinities were developed, including SS1-(dsFv)-PE38, which showed killing activity of tumor cells in vitro (Hassan, R., et al., Clin. Cancer Res. (2002) 8(11): 3520) as well as potency in a murine model of human mesothelin-expressing tumors (Fan, D., et al., Mol. Cancer. Ther. (2002) 1(8): 595). These data validate mesothelin as a suitable target for immunotherapy of multiple cancers. However, in clinical trials, SS1-(dsFv)-PE38 was immunogenic, preventing a second administration for the majority of patients. Furthermore, SS1-(dsFv)-PE38 has been shown to have a fast blood clearance and attempts are being reported to increase the molecular weight by pegylating the fusion protein (Filpula, D., et al., Bioconjugate Chem. (2007) 18(3): 773).
MS-1, MS-2 and MS-3 are mesothelin-binding antibodies which elicit immune effector activity at the cell surface due to their human IgG1 isotype and internalize into mesothelin expressing cells (WO 2006/099141 A2). One of these antibodies, the unconjugated IgG anti-mesothelin antibody MOR Ab 009 is currently being tested in a clinical trial for therapeutic effects in the treatment of pancreatic cancer.
The predictive value of xenograft murine cancer models for clinical outcome of immunotoxin cancer therapy is often limited by a lack of cross-reactivity of the therapeutic antibodies with their murine homologues, which leads to reduced unspecific binding to normal tissue. On the other hand, neutralizing anti-mouse Fv antibodies which are formed in patients being treated with murine or chimeric antibodies may result in either dose-limiting toxicity or diminished therapeutic potency. Thus, to fully exploit the potential of specific mesothelin expression in cancer therapy, targeting antibodies are required which combine the advantages of increased affinities and reduced dissociation rates with a fully human variable chain format, and with murine cross-reactivity.
A further necessary feature of novel antibodies is invariant affinity to different cancer cell lines expressing mesothelin on their surface. Mesothelin is a highly variable protein, undergoing post-translational proteolytic digestion as well as glycosylation at multiple sites (Hassan, R., et al., Clin. Cancer Res. (2004) 10(12 Pt 1): 3937). Variability extends to the transcriptional level, since three different splice variants have been detected, although transcript variant 1 (NM—005823) seems to represent the major species present in tumor cell lines tested so far (Muminova, Z. E., et al., BMC Cancer (2004) 4:19; Hellstrom, I., et al., Cancer Epidemiol. Biomarkers Prev. (2006) 15(5):1014). Thus, effective anti-mesothelin antibodies must bind to an epitope invariantly presented by tumor cells from different patients, independently of individual variance including, but not restricted to, variances in glycosylation patterns, which leads to the expression of different forms of mesothelin.
Provided herein are antibodies, antigen-binding antibody fragments thereof, or variants thereof, that bind to mesothelin with high and invariant affinity, internalize efficiently, and that are preferably cross-reactive to mesothelin from another species. Also provided are antibody-based therapies for cancer, in particular for mesothelin expressing tumors, for example pancreatic, ovarian, or lung cancer, using antibodies, antigen-binding antibody fragments thereof, or variants thereof, that facilitate delivery of therapeutically active agents to cancer cells.